Jet propulsion nozzle with noise reducing means



Aug. 29, 1961 D. M. BROWN 2,998,092

JET PROPULSION NOZZLE WITH NOISE REDUCING MEANS Filed Oct. 14, 1957 2 Sheets-Sheet l j j flaw .IWI W Aug. 29, 1961 D. M. BROWN 2,998,092

JET PROPULSION NOZZLE WITH NOISE REDUCING MEANS Filed Oct. 14, 1957 2 Sheets-Sheet 2 United States Patent 2,998,092 JET PROPULSION NOZZLE WITH NOISE REDUCING MEANS David Morris Brown, Alvaston, England, assignor to Rolls-Royce Limited, Derby, England, a British com- Eiled Oct. 14, 1957, Ser. No. 689,921 Claims priority, application Great Britain Oct. 18, 1956 Claims. (Cl. 181-4 1) This invention comprises improvements in or relating to jet propulsion nozzles.

This invention is concerned with jet propulsion nozzles, for example as set forth in US. Patent No. 2,982,092, issued May 2, 1961, to John Michael Storer Keen, constructed to afford from adjacent the nozzle inlet at least to the throat thereof a plurality of paths for the hot gas flowing through the nozzle, the number of such paths being selected to reduce the noise level in operation of the nozzle as compared with an equivalent nozzle of common construction which for example in the case of a convergent nozzle is a frusto-conical tube. The paths are conveniently formed by attaching elements which taper in the upstream direction, to the inner surface of a tubular wall; such elements at their downstream ends extend radially inwardly either to the nozzle axis in which case the paths have sector-shaped outlets, or only part way towards the nozzle axis in which case the periphery of the outlet appears corrugated.

According to the present invention, in a nozzle as set forth, each of the elements defining the gas paths includes a pair of circumferentially-facing walls bounding the adjacent gas paths and an axially-facing wall joining the downstream ends of the circumferentially-facing walls, so that at the outlet of the nozzle the gas paths alternate with the axially-facing walls around the nozzle, and the circumferentially-facing walls have axial extensions beyond the outlet of the nozzle to delay mixing of hot gases leaving the nozzle and air flowing into the zones behind the axially-facing walls.

Preferably the extensions extend in the radial direction outwardly beyond the perimeter of the nozzle.

Two constructions of jet propulsion nozzle according to this invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is an axial section through one construction,

FIGURE 1A is a perspective view showing the construction of one of the members 12 of FIGURE 1.

FIGURE 2 is a view in the direction of arrow 2 on FIGURE 1 and shows the section line 11 for FIGURE 1, and

FIGURES 3 and 4 are corresponding views of the second construction.

Referring to FIGURES 1 and 2, the nozzle illustrated is a convergent nozzle and comprises an outer tubular Wall -of frusto-conical form and a series of elements 12 (in this case six) attached to the inner surface of the wall 10 to define a corresponding series of trough-like paths for the hot gases leading from adjacent the inlet 10a of the nozzle to the outlet 10b. Each of the elements 12 has a pair of circumferentially-facing walls 12a bounding the trough-like gas paths and an axially-facing end wall 12!), so that the end walls 12b alternate with the ends of the trough-like paths at the outlet 10b. The elements 12 are of tetrahedron form and are of such dimensions that the total cross-sectional area for gas flow through the nozzle decreases gradually from the inlet 10a to provide a throat at the outlet 10b. Also at their downstream ends the elements 12 extend to the nozzle axis. Such a nozzle has a lower noise level as compared with an equivalent simple frusto-conical nozzle.

2,998,992 Patented Aug. 29, 1961 In order to delay mixing of the hot gas issuing from the nozzle with air flowing into the zones behind the walls 12b, the walls 12a are provided with extensions beyond the outlet 10b of the nozzle. The extension walls 120 are contained in axial planes and extend radially from the nozzle axis to beyond the perimeter of the nozzle at its outlet.

Referring now to FIGURES 3 and 4, there is shown a construction of nozzle in which the elements 12 forming the trough-like paths leading to the throat at the nozzle outlet 10b do not extend to the nozzle axis at their downstream ends. Each element has a pair of circumferentially-facing walls 12d, and inwardly-facing wall 12e joining the inner edges of the walls 12d and an axially-facing end wall 12 joining the downstream ends of the walls 12d, and 12e.

In this construction, there are provided axial extensions 12g of the walls 12d to delay mixing of the hot gas issuing from the nozzle and air entering the zones behind the walls 12]. The extension walls 12g are contained in axial planes and extend radially from the inner edges of the walls 12d to beyond the perimeter of the nozzle at its outlet.

The invention is applicable not only to convergent nozzles but also to convergent/divergent nozzles having trough-like paths running through both sections of the nozzle and in this case the extension walls will be downstream of the outlet from the divergent section of the nozzle.

It is thought that by delaying the mixing of the hot gas and the air entering the zones behind the axially-facing end walls, the drag of the nozzle will be reduced.

I claim:

1. A jet propulsion nozzle comprising a tubular outer wall and a series of angularly-spaced elements extending radially inwards from the inner surface of the tubular outer wall to define from adjacent the nozzle inlet at least to the throat thereof a plurality of paths for the hot gas flowing through the nozzle, the number of such paths being selected to reduce the noise level in operation of the nozzle, wherein each of the elements defining the gas paths includes a pair of angularly-spaced circumferentially-facing walls bounding the adjacent gas paths and an axially-facing wall joining the downstream ends of the circumferentially-facing walls, so that at the outlet of the nozzle the gas paths alternate with the axially-facing walls around the nozzle, and the circumferentially-facing walls have axial extensions beyond the outlet of the nozzle to delay mixing of hot gases leaving the nozzle and air flowing into the zones behind the axiallyfacing walls.

2. A jet propulsion nozzle according to claim 1, wherein the extensions extend in the radial direction outwardly beyond the perimeter of the nozzle.

3. A jet propulsion nozzle according to claim 1, wherein said elements at their downstream ends extend radially to the axis of the nozzle and the axial extensions are walls contained in axial planes and extend radially from the nozzle axis to beyond the perimeter of the nozzle.

4. A jet propulsion nozzle according to claim 1, wherein the said elements at their downstream ends project radially part way along towards the nozzle axis and the extensions are walls contained in axial planes and extending radially from the inner edges of the circumferentially-facing walls to beyond the perimeter of the nozzle.

5. A jet propulsion nozzle comprising a tubular outer wall and a series of angularly-spaced elements extending radially inwards from the inner surface of the tubular outer wall to define from adjacent the nozzle inlet at least to the throat thereof a plurality of paths for the hot gas flowing through the nozzle, the number of such paths being selected to reduce the noise level in operation of the nozzle, wherein each of the elements defining the gas paths includes a pair of angularly-spaced circumferentially-facing walls bounding the adjacent gas paths, the angular spacing of said pair of walls of each of the angularly-spaced elements being substantially equal to the angular spacing of the angularly-spaced elements, and each of the elements further comprising an axiallyfacing wall joining the downstream ends of the circumferentially-facing walls, so that at the outlet of the nozzle the gas paths alternate with the axially-facing walls around the nozzle, and the circumferentially-facing walls have axial extensions beyond the outlet of the nozzle to delay mixing of hot gases leaving the nozzle and air flowing into the Zones behind the axially-facing walls.

4 References Cited in the file of this patent UNITED STATES PATENTS 2,382,386 Arms Aug. 14, 1945 2,648,192 Lee Aug. 11, 1953 2,664,700 Benoit Jan. 5, 1954 2,685,936 Brenneman et a1 Aug. 10, 1954 FOREIGN PATENTS 507,357 Italy Dec. 29, 1954 OTHER REFERENCES Flight, Reduction of Jet Noise, July 8, 1955, volume 68, No. 2424, p. 57-60. 

